The cooling system of an internal combustion engine generally comprises two coolant circuits. A bypass circuit, also referred to as a short circuit, returns the coolant to the internal combustion engine without cooling. In the radiator circuit the coolant first flows through a heat exchanger referred to as a radiator before being returned to the internal combustion engine. In the heat exchanger excess heat is dissipated and given off to a secondary coolant. The two cooling circuits of the internal combustion engine may be activated simultaneously or with a time lag. By specifically distributing the coolant flow to both circuits the internal combustion engine is adjusted in the optimum coolant temperature range. This primarily serves to ensure that the admissible temperature limits for the engine and the transmission are adhered to. In addition, account also has to be taken of the competing demands for an optimum warm-up with minimal fuel consumption and a rapid interior climate control. In modern state-of-the-art cooling systems this is usually implemented through flexibly activated components, such as an electrical coolant pump, the speed of which is not fixedly coupled to the speed of the crankshaft, and an electrically activated map-controlled thermostat, electrical fan and heating valves. It is thereby possible to design the cooling system for the aforementioned boundary conditions including a flexible heat management. Intelligent heat management moreover also makes it possible to reduce the fuel consumption and pollutant emissions. An externally cooled exhaust gas recirculation and the shortening of the warm-up phase through coolant stoppage and an isolation of thermal masses are particularly suited to this purpose. These objectives can be achieved by adjusting the coolant temperature to the prevailing load range of the internal combustion engine with the aid of a heat management module.
U.S. Pat. No. 4,644,909 discloses such a heat management module. The heat management module comprises a valve mechanism, which serves to control a radiator circuit and/or a bypass circuit of a cooling system. This is done by means of an electric motor, which can be controlled by an electronic control, which on the input side analyzes the signal from a coolant temperature sensor in order to actuate the valve mechanism as a function of the prevailing coolant temperature, so that the mixing ratio of the coolant between the cooling circuits is adjusted on the basis of a preset coolant temperature. The valve mechanism comprises a valve spool, which performs either a linear or a rotational switching motion. Accordingly, the electric motor drive is embodied either as a linear drive, for example in the form of a proportional magnet, or as an electric stepping motor for generating the rotational switching motion.
DE 198 49 492 A1 discloses a further heat management module, which comprises a valve member for controlling a bypass circuit and a radiator circuit of a cooling system. In this state of the art the valve member is embodied as a rotary spool, which is driven by an electric motor. The electric motor drive serves to bring the valve member selectively into a closed position for the radiator circuit and the bypass circuit, or into an open position between the radiator circuit or the bypass circuit. In addition, it is also possible to produce a mixed operation by simultaneously connecting the radiator circuit and the bypass circuit to the discharge connection, in order to achieve a heat management within the cooling circuit through a map-controlled cooling. By selecting a suitable switching position of the valve mechanism, an optimum coolant temperature is possible for any operating state of the internal combustion engine, which leads to the reduction in fuel consumption and pollutant emissions mentioned in the introduction whilst at the same time protecting the internal combustion engine.